Liquid/vapor absorption systems using ammonia refrigerant, referred to as ammonia-water or aqua-ammonia systems, are well known in the art. These systems utilize absorber heat exchange or generator/absorber heat exchange (GAX) cycles for supplying cooling, and heating to an indoor coil and other heat exchange components exposed to the space or load to be conditioned. Examples of aqua-ammonia absorption heat pumps using GAX cycles are disclosed in U.S. Pat. Nos. Re. 36,684, 5,367,884 and Modahl et al., xe2x80x9cEvaluation of a Commercial Advanced Absorption Heat Pump Bread Board,xe2x80x9d 1988. In such apparatus, a solution pump is used to pump ammonia-rich absorption fluid from the absorber assembly to the generator assembly, and maintains pressure differentials between the low pressure, absorber side to the high pressure, generator side of the absorption system apparatus. Diaphragm pumps using a hydraulically driven diaphragm are commonly used as solution pumps. Such hydraulic diaphragm pumps rely on internal pressures of the system and atmospheric pressure for returning the diaphragm and for cycling operation of the pump. Moreover, due to internal pump friction, such pumps are capable of operating only at atmospheric pressures above about 1.1-1.2 atmospheres. Although such pumps function adequately where the system operates to provide cooling and at relatively high ambient temperatures with relatively high suction pressures, e.g., 55 to 100 psia, at low temperature heating operations, with relatively low solution pressures, e.g., as low as 8 psia, such presently used hydraulic diaphragm pumps often do not perform. Correspondingly, presently used diaphragm pumps do not operate efficiently, if at all, at solution temperatures below 35xc2x0 F. thereby substantially limiting their use for low temperature condition heat pumping and refrigeration.
The apparatus described herein uses a plunger-driven diaphragm solution pump in an absorption fluid loop for pumping absorption fluid having an ammonia concentration of between about 20% and about 60% by weight, from the absorber assembly to the generator assembly. Such a solution pump is capable of operating at high discharge temperatures and pressures to provide cooling as well as at low pressures where the heat pump system operates to provide heating.